Interference caused by other users or systems and noise sum into a signal on the radio path. Radio systems therefore employ different diversity methods to increase the coverage area and/or capacity of the system. One of them is spatial diversity, which is obtained using an array antenna comprising a plural number of antenna elements that are physically separate from each other. The received signals are combined in diversity receivers that employ maximal-ratio combining, for example.
Current receivers are based on statistical signal models the accuracy of which cannot be relied on in all situations. The impact of noise and interference can be reduced in the Maximal Ratio Combining (MRC) method, for example. However, this method supposes that the interference and noise in each antenna element are independent of other antenna elements, i.e. they are white. In actual cellular radio networks this is not always true; for example, the interference that high-power signals, a few at the most, cause upon reception may affect all the antenna elements, i.e. the interference in the antenna elements is coloured.
Interference Rejection Combining (IRC) is a method that does not contain assumptions about whether interference and noise correlate with antenna elements. A disadvantage of the IRC method is that it occupies more baseband processing capacity than the MRC method, because there are more parameters to be estimated although the sample group available is the same. When used extensively, baseband processing may reduce the ability of the base station to serve the subscriber terminals and, thereby, it may impair cell capacity. Due to errors that may take place in parameter estimation if the number of parameters to be estimated is large, the use of complex interference elimination methods may even degrade the capacity of the receiver.